The present invention relates to ink supply for printers and, in particular, it concerns a hydraulic shock absorber for absorbing shock waves in an ink supply line caused by motion of a print head.
It is known to employ an arrangement of one or more inkjet print heads in a scanning motion to achieve full print coverage across the width of a substrate. In order to minimize the size and weight of the moving components, it is preferable that ink be supplied to the print head from a stationary ink reservoir. This is typically achieved by use of a flexible tube connecting from the reservoir to the moving print head. The tube must be sufficiently flexible to allow bending to accommodate the range of movement of the print head while being sufficiently resilient to support itself against the slight negative pressure under which ink is provided to conventional inkjet print heads.
While reducing the weight of the moving components, the use of an external ink reservoir and flexible supply tube present certain problems. Specifically, the sudden stopping and starting of the print head at each end of its scanning motion produces shock waves through the ink in the supply tube. These shock waves may interfere with the droplet ejection mechanism by partially emptying ink from the nozzles, or may cause ink leakage from the nozzles.
A further problem associated with flexible ink supply tubes is the variation of internal volume which occurs on flexing of the tube. A given length of tube has a smaller internal volume when bent than when in an unflexed state. As a result, the volume of ink contained within the supply tube varies as the print head passes across the substrate, causing cyclic pressure variations in the ink supply and requiring wasteful reverse flow from the supply tube back to the reservoir.
There is therefore a need for a shock absorber for an ink supply line which will damp shock waves through the ink within an ink supply line associated with an inkjet print head. It would also be highly advantageous to provide a shock absorber which would help to compensate for volume variations within an ink supply tube during motion of an inkjet print head.
The present invention is a hydraulic shock absorber for connection within an ink supply line for supplying ink from a stationary ink reservoir to at least one moving inkjet print head.
According to the teachings of the present invention there is provided, a hydraulic shock absorber for connection within an ink supply line which is connected so as to supply ink from a stationary ink reservoir to at least one moving inkjet print head, the shock absorber comprising: (a) a conduit having at least one wall defining an inlet, an outlet and a contained volume, at least part of the wall being readily deformed by variations in a pressure differential across the part of the wall so as to vary the contained volume; and (b) a collapse prevention element deployed within the conduit and configured to prevent deformation of the part of the wall in a manner which would obstruct passage through the conduit from the inlet to the outlet.
According to a further feature of the present invention, the part of the wall is implemented as a deformable tube.
According to a further feature of the present invention, the collapse prevention element is implemented as a helical coil at least part of which is deployed within the deformable tube.
According to a further feature of the present invention, the deformable tube, when in an undeformed cylindrical state, has an internal diameter D1, and the helical coil has an external diameter D2, D1 being at least about 10% greater than D2.
According to a further feature of the present invention, the part of the wall is implemented using flexible material having a gas permeability significantly less than that of silicone.
According to a further feature of the present invention, the part of the wall is implemented using material sufficiently flexible such that, in the absence of the collapse prevention element, the conduit would be substantially closed by collapse of the part of the wall when ambient pressure exceeded a pressure within the contained volume by in excess of about 150 mm, and preferably about 30 mm, head of water.